Argentina–Uruguay

The boundary between Argentina and Uruguay begins at the tripoint with Brazil and follows the Uruguay River and then the Río de la Plata southeastwards to the Atlantic Ocean. Uruguay was created as a buffer state between Argentina and Brazil in 1828 and has maintained positive and peaceful relations with Argentina since its independence. Though the 830 kilometer (516 mile) boundary is one of the earliest de facto boundaries in South America, it was one of the last to be formally agreed upon in 1961. The two States have completed some demarcation works and bilaterally manage the boundary rivers.

Argentina and Uruguay also have an established maritime boundary.